Valve control apparatus for internal combustion engine

ABSTRACT

A valve control apparatus for an internal combustion engine is provided which is capable of optimally setting the closing timing of an engine valve according to operating conditions of the engine while suppressing an increase in the inertial mass of the engine valve to the minimum, thereby attaining improvement of fuel economy, and realization of higher engine rotational speed and higher power output in a compatible fashion, and reducing costs and weight thereof. The valve control apparatus controls opening and closing operations of an engine valve. A cam-type valve actuating mechanism actuates the engine valve to open and close the engine valve, by a cam which is driven in synchronism with rotation of the engine. An actuator makes blocking engagement with the engine valve having been opened, to thereby hold the engine valve in an open state. An ECU controls operation of the actuator to thereby control closing timing of the engine valve.

RELATED APPLICATIONS

This application is a 35 U.S.C. 371 national stage filing ofInternational Application No. PCT/JP02/07624, filed 26 Jul. 2002, whichclaims priority to Japan Patent Application No. 2001-226709 filed on 26Jul. 2001, in Japan and Japan Patent Application No. 2002-211325 filedon 19 Jul. 2002, in Japan. The contents of the aforementionedapplications are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a valve control apparatus for controllingopening and closing operations of intake valves and/or exhaust valves,more particularly for controlling valve-closing timing thereof.

BACKGROUND ART

Conventionally, with a view to improving fuel economy and power outputof an internal combustion engine and reducing exhaust emissionstherefrom, various kinds of valve control apparatuses have been proposedwhich variably control the opening and closing timing or the valve liftof intake valves and/or exhaust valves so as to attain intake andexhaust performance suitable for operating conditions of the engine. Asone of such conventional valve control apparatuses, a type is knownwhich changes the phase of an intake cam with respect to a camshaft tothereby continuously change the opening and closing timing of an intakecam (e.g. Japanese Laid-Open Patent Publication (Kokai) No. 7-301144).In this type of valve control apparatus, however, the intake valve opensover a fixed valve-opening time period, so that when the opening timingof the intake valve is determined, the closing timing thereof isautomatically determined. This makes it impossible to attain the optimumvalve-opening timing and the optimum valve-closing timing at the sametime for all regions of the rotational speed of the engine and load onthe same which change steplessly.

Further, as another type of conventional valve control apparatus (e.g.Japanese Laid-Open Patent Publication (Kokai) No. 62-12811) is known inwhich each of an intake cam and an exhaust cam is formed by a high-speedcam and a low-speed cam having respective predetermined cam profilesdifferent from each other, and each cam is switched between thelow-speed cam and the high-speed cam for use in low rotational speed andhigh rotational speed of the engine, respectively. In this type of valvecontrol apparatus, however, the cam profile is changed between twostages, and hence the opening and closing timing and valve lift of theintake/exhaust valve are also merely changed between two stages.Therefore, this apparatus is also not capable of attaining the optimumvalve-opening/closing timing and valve lift for all regions of therotational speed and load.

Further, still another type of a valve control apparatus (e.g. JapaneseLaid-Open Patent Publication (Kokai) No. 8-200025) is known which useselectromagnets to open and close intake valves and exhaust valves. Inthis valve control apparatus, two intake valves and two exhaust valvesare provided for each cylinder, and these four intake and exhaust valvesare actuated by respective electromagnetic valve actuating mechanisms(hereinafter, this valve control apparatus is referred to as “thefully-electromagnetic valve control apparatus”). Each electromagneticvalve actuating mechanism is comprised of a pair of electromagnetsopposed to each other, an armature arranged between the electromagnetsand connected to the intake/exhaust valve associated therewith, and twocoil springs urging the armature. In this electromagnetic valveactuating mechanism, the energization of the two electromagnets iscontrolled to cause the armature to be attracted to one of theelectromagnets in an alternating fashion to thereby open and close theintake/exhaust valve. Therefore, by controlling the timing ofenergization, the opening and closing timing of the intake/exhaust valvecan be controlled as desired, whereby it is possible to realize theoptimum opening and closing timing for all regions of the rotationalspeed and load and optimize fuel economy, power output, etc. It shouldbe noted that when the two electromagnets are not energized, thearmature is held in a neutral position by the balance of the urgingforces of the two coil springs. In this fully-electromagnetic valvecontrol apparatus, however, all the intake/exhaust valves are eachactuated by the electromagnetic valve actuating mechanism, so that theelectric power consumption becomes very large, which reduces the effectsof the improved fuel economy. Further, the electromagnets and armatureof the electromagnetic valve actuating mechanism are formed by magneticsubstances, which results in an increase in weight and manufacturingcost of the apparatus.

As a solution to this problem, the present applicant has alreadyproposed by Japanese Patent Application No. 20001-012300 a valve controlapparatus (hereinafter referred to as “the first valve controlapparatus”) which actuates only one of two intake valves provided forone cylinder by an electromagnetic valve actuating mechanism similar tothat described above, and the other of the intake valves and exhaustvalves by cam-type valve actuating mechanisms operating in synchronismwith rotation of the engine. In this first valve control apparatus, theopening timing and the closing timing of the one of the intake valvesare set as desired according to operating conditions of the engine byusing the electromagnetic valve actuating mechanism, whereby the optimumopening and closing timing can be realized, and the improvement of thefuel economy and the enhancement of the power output are madecompatible. Further, compared with the fully-electromagnetic valvecontrol apparatus, the number of electromagnetic valve actuatingmechanisms is reduced to one fourth, which contributes to the fueleconomy through reduction of electric power consumption, and reductionof weight and manufacturing costs.

Another valve control apparatus proposed by the present applicant isalso known which is disclosed in Japanese Laid-Open Patent Publication(Kokai) No. 63-289208 (hereinafter referred to as “the second valvecontrol apparatus”). The second valve control apparatus includes acam-type valve actuating mechanism for opening and closing an intakevalve via a rocker arm by using a cam provided on a camshaft, and anelectromagnetic actuator for holding the intake valve in an openposition. This electromagnetic actuator is comprised of one solenoidfixed to a cylinder head, an armature fixed to a valve stem of theintake valve, and an impact-absorbing spring arranged between thearmature and a retainer, and according to operating conditions of theengine, energizes the solenoid when the intake valve has reached theopen position to cause the attractive force to act on the armature,whereby the intake valve is held in the open position to control theclosing timing of the intake valve.

However, although the first valve control apparatus alleviates theproblem suffered by the fully-electromagnetic valve control apparatus,due to its use of the electromagnetic valve actuating mechanism for partthereof, there still remains room for improvement in the followingpoints: This valve control apparatus necessitates one electromagneticvalve actuating mechanism for one cylinder, and hence two electromagnetsfor one cylinder. This results in increased electric power consumption,and decreases the advantageous effects of improvement of fuel economythanks to the variable opening and closing timing of the intake valve,and compared with the ordinary cam-actuated type valve controlapparatus, the weight and manufacturing costs are still large. Further,the maximum rotational speed of the engine available through the use ofthe electromagnetic valve actuating mechanisms is substantiallydetermined by a spring constant of each coil spring. This makes itnecessary to set the spring constant of the coil spring to a large valueand accordingly electromagnets providing large attractive forces arealso required to be employed, when the apparatus is applied to aninternal combustion engine whose maximum rotational speed is high (e.g.about 9000 rpm). This results in an increased electric powerconsumption, and degrades fuel economy in low-to-medium rotational speedoperating regions in which the engine is usually operated morefrequently than in other regions, and makes it difficult to attain theimprovement of fuel economy and the realization of higher rotationalspeed and higher power output in a compatible fashion.

Further, the second valve control apparatus is only required to arrangeone electromagnet for one intake valve of each cylinder, and thereforehas advantages over the first valve control apparatus in that it canfurther reduce the electric power consumption and improve the fueleconomy. However, there remains room for improvement in the followingpoints: In the second valve control apparatus, irrespective of whetherthe electromagnetic actuator is active or inactive, the weight of thearmature and the spring force of the impact-absorbing spring always acton the intake valve. This increases the inertial mass of the intakevalve in the inactive state of the electromagnetic actuator, whichrestricts the maximum engine rotational speed and the maximum poweroutput. In this case, to increase the maximum engine rotational speed,it is necessary to increase the spring constant of the valve spring.This degrades fuel economy due to an increase in electric powerconsumption, and makes it impossible to attain the improvement of fueleconomy and the realization of higher engine rotational speed and higherpower output in a compatible fashion, or sufficiently reduce the weightand manufacturing costs. Further, in the case of this valve controlapparatus, to mount the solenoid, the armature, the impact-absorbingspring therein, it is necessary to modify the designs of the cylinderhead and intake valves, at inevitably very high expenses.

This invention has been made with a view to providing a solution tothese problems, and an object thereof is to provide a valve controlapparatus for an internal combustion engine that is capable of optimallysetting the closing timing of an engine valve according to operatingconditions of the engine while suppressing an increase in the inertialmass of the engine valve to the minimum, thereby attaining improvementof fuel economy, and realization of higher engine rotational speed andhigher power output in a compatible fashion, and reducing costs andweight thereof.

DISCLOSURE OF INVENTION

To attain the above object, the invention provides a valve controlapparatus for an internal combustion engine for controlling opening andclosing operations of an engine valve, the valve control apparatuscomprising a cam-type valve actuating mechanism that actuates the enginevalve to open and close the engine valve, by a cam which is driven insynchronism with rotation of the engine, an actuator that makes blockingengagement with the engine valve having been opened, to thereby hold theengine valve in an open state, and control means for controllingoperation of the actuator to thereby control closing timing of theengine valve.

According to this valve control apparatus for an internal combustionengine, the engine valve is opened and closed by a cam driven insynchronism with rotation of the cam-type valve actuating mechanism.Further, under the control of the control means, the actuator makesblocking engagement with the engine valve having been opened so as tohold the same in the open state, and further, by canceling the holding,the closing timing of the engine valve is controlled.

As described above, according to this invention, while actuating theengine valve by the cam-type actuating mechanism, the actuator isoperated as required, whereby the closing timing of the engine valve canbe controlled as desired. This makes it possible to attain the optimumfuel economy and power output adapted to operating conditions of theengine. For instance, when the engine valve is an intake valve, in alow-rotational speed/low-load condition, the closing timing of theintake valve is controlled to late closing according to the operatingconditions of the engine, thereby reducing the pumping loss of theintake valve to the minimum, whereby the fuel economy can be enhanced.On the other hand, in the high-rotational speed/high-load region, theactuator is made inactive, and only the cam-type valve actuatingmechanism actuates the intake cam, whereby the higher rotational speedand higher power output can be attained without being affected by thefollow-up capability of the actuator. Further, when the engine valve isan exhaust valve, by varying the closing timing of the exhaust valve,the overlap amount is controlled, whereby the power output can beimproved and the exhaust emissions can be reduced.

Further, the engine valve is basically actuated by the cam-typeactuating mechanism, and the actuator is only required to make blockingengagement with the engine valve in one direction, which allows theapparatus to be simplified in construction. Further, since the actuatorcan be operated only when necessary, the energy saving can be attained,and the fuel economy can be further enhanced by this feature. Further,since the engine valve can be actuated by the cam-type actuatingmechanism alone, even when a fail occurred on the actuator, the fail canbe easily coped with.

Preferably, the valve control apparatus as recited in claim 1 furthercomprises operating condition-detecting means for detecting operatingconditions of the engine, and the control means controls the operationof the actuator according to the detected operating conditions of theengine.

According to this preferred embodiment, the operation of the actuator iscontrolled according to the detected operating conditions of the engine.This makes it possible to set the active or inactive state of theactuator and the closing timing of the engine valve optimally accordingto actual operating conditions of the engine, for all rotational speedregions and load regions.

More preferably, the valve control apparatus as recited in claim 2further comprises a switching mechanism for switching an operation modeof the actuator between an active mode in which the actuator makes theblocking engagement with the engine valve and an inactive mode in whichthe valve actuator does not make the blocking engagement with the enginevalve, and operation mode-determining means for determining theoperation mode of the actuator according to the detected operatingconditions of the engine, and the control means controls operation ofthe switching mechanism according to the determined operation mode.

According to this preferred embodiment, the actuator is switched betweenthe active state and the inactive state, according to the operation modedetermined according to the operating conditions of the engine, so thatthe actuator can be appropriately made active only when necessaryaccording to the actual operating conditions of the engine. Further,when the operation mode of the actuator is set to the inactive mode, theswitching mechanism places the actuator in a state not brought intoblocking engagement with the engine valve, to thereby forcibly make thesame inactive. Therefore, even when a fail occurred on the actuatoritself, the engine valve can be actuated by the cam-type actuatingmechanism without any trouble, while preventing the fail from adverselyaffecting the operation of the engine valve, which makes it possible toprevent degradation of combustion state and degradation of exhaustemissions.

Further preferably, in the valve control apparatus as recited in claim2, the switching mechanism is formed by a hydraulic switching mechanismfor hydraulically switching the operation mode of the actuator, and thecontrol means causes the actuator to be made inactive when the engine isstarted.

According to this preferred embodiment, the switching mechanism isformed by the hydraulic switching mechanism, and the operation mode ofthe actuator is hydraulically switched between the active mode and theinactive mode. On the other hand, at the start of the engine, it takestime to increase oil pressure, and hence it is impossible to obtainsufficient oil pressure. Therefore, it is difficult for the hydraulicswitching mechanism to operate stably, and hence there is a fear thatthe actuator cannot stably hold the engine valve. Therefore, theactuator is made inactive when the engine is started, and the engine isactuated only by the cam-type valve actuating mechanism, to ensure thestable operation of the engine valve.

Preferably, in the valve control apparatus as recited in any one ofclaims 1 to 4, the actuator is formed by an electromagnetic actuatorcomprising a single electromagnet that has a coil whose energization iscontrolled by the control means, an armature that is attracted to theelectromagnet when the coil is energized, and a stopper providedintegrally with the armature, for being brought into blocking engagementwith the engine vale having been opened, in a state in which thearmature has been attracted to the electromagnet.

According to the preferred embodiment, the actuator is formed by anelectromagnetic actuator. Further, the electromagnetic actuator isconfigured to be brought into blocking engagement with the engine valveby driving the armature only in one direction by the singleelectromagnetic actuator. This makes one electromagnet sufficient forone engine valve, which makes it possible to reduce the weight and costand minimize electric power consumption.

Preferably, the valve control apparatus as claimed in any one of claims1 to 5, further comprises a hydraulic impact-lessening mechanism thatlessens an impact on the engine valve caused by operation of theactuator.

According to this preferred embodiment, the hydraulic impact-lesseningmechanism can lessen the impact received by the engine valve when theengine valve returns to its valve-closing position after cancellation ofthe holding thereof by the actuator, and suppress noise caused by theimpact. Further, if the hydraulic impact-lessening mechanism isemployed, in a very cold oil temperature condition at a very coldtemperature start or a high oil temperature condition in a maximumrotational speed condition, the viscosity of hydraulic oil largelychanges, which can make it impossible to preserve impact-lesseningperformance. Under such server temperature conditions, the actuator canbe made inactive, whereby the impact-lessening performance can be fullyensured.

Further preferably, the valve control apparatus as recited in claim 3,further comprises a rocker shaft, an actuating rocker arm pivotallysupported on the rocker shaft, for being brought into abutment with theengine valve and being driven by the intake cam to actuate the enginevalve to open and close the engine valve, and a holding rocker armpivotally supported on the rocker shaft, for having the actuator broughtinto abutment therewith, to hold the engine valve in the open state, andthe switching mechanism switches the operation mode of the actuatorbetween the active mode and the inactive mode, by switching a state ofthe actuating rocker arm and the holding rocker arm between a connectedstate in which the actuating rocker arm and the holding rocker arm areconnected to each other, and a disconnected state in which the actuatingrocker arm and the holding rocker arm are disconnected from each other.

According to this preferred embodiment, the engine valve is opened andclosed by an actuating rocker arm driven by the intake cam. Further, theactuator is brought into abutment with a holding rocker arm as aseparate member from the actuating rocker arm. Then, in the active modeof the actuator, the holding rocker arm and the actuating rocker arm areconnected by the switching mechanism, whereby the engine is held in theopen state by the actuator via the holding rocker arm and the actuatingrocker arm. Further, in the inactive mode of the actuator, the actuatingrocker arm and the holding rocker arm are disconnected from each otherby the switching mechanism. Thus, when in the inactive mode, theactuating rocker arm is pivotally moved without being adversely affectedby the holding rocker arm and the inertial mass of the actuator in astate completely free from them, which makes it possible to save energy,and improve the follow-up capability of the valve system at highrotational speed.

Still more preferably, in the valve control apparatus as claimed inclaim 7, the actuating rocker arm comprises a plurality of actuatingrocker arms, and the valve control apparatus further comprises a firsthydraulic switching mechanism for hydraulically switching a state of theplurality of actuating rocker arms between a connected state in whichthe plurality of actuating rocker arms are connected to each other and adisconnected state in which the plurality of actuating rocker arms aredisconnected from each other, the switching mechanism being formed by asecond hydraulic switching mechanism, one of the plurality of actuatingrocker arms being formed with an oil chamber for the first hydraulicswitching mechanism, and the holding rocker arm being arranged adjacentto the actuating rocker arm formed with the oil chamber.

According to this preferred embodiment, the holding rocker arm isdisposed in the vicinity of the actuating rocker arm having the oilchamber formed therein for the first hydraulic switching mechanism.Therefore, the oil passages for the first and second hydraulic switchingmechanisms can be arranged close to each other, whereby machining andforming of the oil passages can be facilitated, and oil pressure losscan be reduced.

Still more preferably, in the valve control apparatus as claimed inclaim 7 or 8, an abutment portion of the holding rocker arm with whichthe actuator abuts is disposed at a location remoter from the rockershaft than an abutment portion of the actuating rocker arm with whichthe engine valve abuts is.

According to this preferred embodiment, the abutment portion of theholding rocker arm with which the actuator abuts is disposed at alocation remoter from the rocker shaft as a support of the two rockerarms than the abutment portion of the actuating rocker arm with whichthe engine valve abuts is. Therefore, the holding force of the actuatorrequired for holding the engine valve can be reduced, whereby the sizeof the actuator can be reduced and energy saving can be attained.Further, since the holding rocker arm and the actuating rocker arm areseparate from each other, even if the abutment portion with which theactuator abuts is disposed as above, it is possible to avoid theincrease in the size of the actuating rocker arm, the resulting increasein the inertial mass in the inactive mode.

Still more preferably, in the valve control apparatus as recited inclaim 7 or 8, an abutment portion of the holding rocker arm with whichthe actuator abuts is disposed at a location closer to the rocker shaftthan an abutment portion of the actuating rocker arm with which theengine valve abuts is.

According to this preferred embodiment, the abutment portion of theholding rocker arm with which the actuator abuts is disposed at alocation closer to the rocker shaft than the abutment portion of theactuating rocker arm with which the engine valve abuts is. Therefore,the stroke of the actuator required for holding the engine valve can bereduced. Further, since the holding rocker arm is a separate member fromthe actuating rocker arm, even if the abutment portion with which theactuator abuts is disposed as described above, interference with amember arranged in its vicinity, e.g. the first hydraulic switchingmechanism can be avoided, and hence the actuator can be disposed incompact arrangement in the operating direction thereof.

Also, still more preferably, in the valve control apparatus as recitedin any of claims 7 to 10, the switching mechanism switches a state ofthe actuating rocker arm and the holding rocker arm to a connected statewhen the engine is in a low rotational speed condition, and to adisconnected state when the engine is in a high rotational speedcondition.

According to this preferred embodiment, the holding rocker arm isconnected to the actuating rocker arm at the low rotational speed of theengine, whereas during high rotational speed of the same, the holdingrocker arm is disconnected from the actuating rocker arm. This makes itpossible to avoid the increase in the inertial mass of the actuatingrocker arm particularly during high rotational speed of the engine,whereby the follow-up capability of the valve system can be enhanced.

The above and other objects, features, and advantages of the inventionwill become more apparent from the following detailed description takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram schematically showing the arrangement of avalve control apparatus for an internal combustion engine, according toa first embodiment of the invention;

FIG. 2 is a diagram showing the arrangement of intake valves and exhaustvalves;

FIG. 3 is a side view of an intake valve and a valve control apparatus;

FIG. 4 is a cross-sectional view taken on line IV—IV in FIG. 3;

FIG. 5 is a cross-sectional view of an electromagnetic actuator;

FIG. 6 is a diagram showing an example of operations of intake andexhaust valves performed with the valve control apparatus;

FIG. 7 is a flowchart of a valve control process executed by an ECUappearing in FIG. 1;

FIG. 8 is a flowchart of part of the FIG. 7 valve control process;

FIG. 9 shows an example of an operating region map employed in the FIG.7 valve control process;

FIG. 10 shows an example of an operating region map used in occurrenceof a fail;

FIG. 11 is a flowchart of a control process for controlling anelectromagnetic actuator;

FIG. 12 is a diagram showing an example of settings of valve-closingtiming of a first intake valve in a low engine rotational speedcondition;

FIG. 13 is a side view of a valve control apparatus for an internalcombustion engine, according to a second embodiment of the invention;

FIG. 14 is a cross-sectional view taken on line XIV—XIV in FIG. 13;

FIG. 15 is a cross-sectional view of a valve control apparatus for aninternal combustion engine, according to a third embodiment of theinvention;

FIG. 16 shows a table showing an example of operation settings of firstand second intake valves and an electromagnetic actuator in the FIG. 15valve control apparatus;

FIG. 17 shows an example of an operating region map used for theoperation settings in FIG. 16;

FIG. 18 is a cross-sectional view showing a variation of the valvecontrol apparatus;

FIG. 19 is a cross-sectional view of a valve control apparatus for aninternal combustion engine, according to a fourth embodiment of theinvention;

FIG. 20 is a diagram showing an example of operations of intake andexhaust valves performed with the FIG. 19 valve control apparatus;

FIG. 21 shows a table showing an example of operation settings of firstand second intake valves and an electromagnetic actuator in the FIG. 19valve control apparatus; and

FIG. 22 shows an example of an operating region map used for theoperation settings in FIG. 21.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereafter, a valve control apparatus for an internal combustion engine,according an embodiment of the invention, will be described withreference to drawings. FIG. 1 schematically shows the arrangement of thevalve control apparatus to which the present invention is applied. Aninternal combustion engine (hereinafter referred to as “the engine”) 3shown therein is a four-cylinder (only one cylinder is shown in FIG. 2)in-line DOHC gasoline engine installed on a vehicle not shown. As shownin FIG. 2, each cylinder 4 is provided with first and second intakevalves IV1, IV2, and first and second exhaust valves EV1, EV2, as enginevalves. As illustrated in FIG. 3 showing an example of the first intakevalve IV1, the intake valves IV1, IV2 are arranged such that each ofthem is movable between a closed position (shown in FIG. 3) for closingan intake port 3 a of the engine 3 and an open position (not shown)projected into a combustion changer 3 b, for opening the intake port 3a, while being urged by a coil spring 3 c toward the closed position.

As shown in FIG. 1, the valve control apparatus 1 comprises a cam-typevalve actuating mechanism 5 provided on an intake side for opening andclosing the two intake valves IV1, IV2, and a cam-type valve actuatingmechanism 6 provided on an exhaust side for opening and closing the twoexhaust valves EV1, EV2, a variable valve-closing timing device 7 forvarying the closing timing of the first intake valve IV1, a camprofile-switching mechanism 13 for switching between cam profiles of anintake cam 11, referred to hereinafter, of the cam-type valve actuatingmechanism 6, and an ECU 2 (control means) for controlling operations ofthese devices.

The cam-type valve actuating mechanism 5 on the intake side is comprisedof a camshaft 10, the intake cam integrally formed on the camshaft 10,and a rocker arm 12 which is driven by the intake cam and pivotallymovable for converting the rotating motion of the camshaft 10 intoreciprocating motions of the intake valves IV1, IV2. The camshaft 10 isconnected to a crankshaft, not shown, of the engine 3 via a drivensprocket and a timing chain (none of which is shown), and driven by thecrankshaft, for rotation such that it performs one rotation per tworotations of the crankshaft.

As shown in FIG. 1, the intake cam 11 is comprised of a low-speed cam 11a, an inactive cam 11 b having a very low cam nose, and a high-speed cam11 c disposed between the two cams 11 a, 11 b and having a higher camprofile than that of the low-speed cam 11 a. The rocker arm 12 iscomprised of a low-speed rocker arm 12 a, an inactive rocker arm 12 b,and a high-speed rocker arm 12 c, as actuating rocker arms. Theselow-speed, inactive, and high-speed rocker arms 12 a to 12 c arepivotally mounted on a rocker shaft 14, and arranged in a mannerassociated with the low-speed, inactive, and high-speed cams 11 a to 11c of the intake cam 11, respectively, such that these cams 11 a to 11 care in slidable contact therewith via respective rollers 15 a to 15 c.The low-speed rocker arm 12 a and the inactive rocker arm 12 b are inabutment with the upper ends of the first intake valve IV1 and thesecond intake valve IV2, respectively. Further, the rocker shaft 14 isformed with two lines of oil passages: a first oil passage 16 a for acam profile-switching mechanism 13, and a second oil passage 16 b forthe variable valve-closing timing device 7 (see FIG. 4).

The cam profile-switching mechanism (hereinafter referred to as “theVTEC”) 13 is comprised of a first switching valve 17 for hydraulicallyswitching between connection and disconnection of the low-speed andinactive rocker arms 12 a, 12 b and the high-speed rocker arm 12 c, anda first oil pressure-switching mechanism 18 for switching between thesupply and cut-off of the oil pressure to the first switching valve 17.

As shown in FIG. 4, the first switching valve 17 is formed by a pistonvalve, and has cylinders 19 a to 19 c formed continuous with each otherat respective locations corresponding to the rollers 15 a to 15 c of thelow-speed, inactive, and high-speed rocker arms 12 a to 12 c, andpistons 20 a to 20 c slidably arranged within these cylinders 19 a to 19c, respectively, and in axial abutment with each other. The piston 20 ahas an oil chamber 21 formed therein on a side remote from the inactiverocker arm 12 b, and a coil spring 22 is arranged between the piston 20b and the cylinder 19 b, for urging the piston 20 b toward the low-speedrocker arm 12 a.

Further, the oil chamber 21 is communicated with the first oilpressure-switching mechanism 18 via an oil passage 23 formed through thelow-speed rocker arm 12 a, and the first oil passage 16 a formed throughthe rocker shaft 14. The first oil pressure-switching mechanism 18 iscomprised of an electromagnet valve and a spool (none of which isshown), and connected to an oil pump (not shown). The mechanism 18 isdriven by a control signal from the ECU 2, for switching between thesupply and cut-off of the oil pressure to the first switching valve 17via the first oil passage 16 a.

According to the above configuration, when the supply of oil pressurefrom the first oil pressure-switching mechanism 18 to the firstswitching valve 17 is cut off, the pistons 20 a to 20 c of the firstswitching valve 17 are held in respective positions shown in FIG. 4 bythe urging force of the coil spring 22, and engaged only with thecylinders 19 a to 19 c, respectively. Therefore, the low-speed,inactive, and high-speed rocker arms 12 a to 12 c are disconnected fromeach other, and hence rotate independently of each other. As a result,with rotation of the camshaft 10, the low-speed rocker arm 12 a isdriven by the low-speed cam 11 a, whereby the first intake valve IV1 isopened and closed in low-speed valve timing corresponding to the camprofile of the low-speed cam 11 a (hereinafter referred to as “Lo.V/T”), while the inactive rocker arm 12 b is driven by the inactive cam12 b, whereby the second intake valve IV2 is opened and closed ininactive valve timing by a slight valve lift corresponding to the camprofile of the inactive cam 11 b (hereinafter referred to as “inactiveV/T”). It should be noted that in the above case, although thehigh-speed rocker arm 12 c is also driven by the high-speed cam 11 c,since the first switching valve 17 mechanically disconnects between thehigh-speed rocker arm 12 c and the low-speed rocker arm 12 a and betweenthe high-speed rocker arm 12 c and the inactive rocker arm 12 b, theoperation of the high-speed rocker arm 12 c does not affect theoperations of the first and second intake valves IV1, IV2. Hereafter,such an operation mode of the two intake valves IV1, IV2 by the VTEC 13is referred to as “Lo.-inactive V/T mode” as required. In theLo.-inactive V/T mode, a swirl is produced in the cylinder 4, whichflows from the first intake valve IV1 toward the second intake valveIV2, which ensures stable combustion even when the mixture is lean.

On the other hand, although not shown, when the oil pressure is suppliedfrom the first oil pressure-switching mechanism to the oil chamber 21 ofthe first switching valve 17, the pistons of the first switching valve17 are slid toward the coil spring 22 against the urging force thereof,whereby the piston 20 a is engaged with the cylinders 19 a and 19 c in abridging fashion, and at the same time the piston 20 c in the center isengaged with the cylinders 19 b, 19 c in a bridging fashion. Thisconnects the low-speed and inactive rocker arms 12 a, 12 b with thehigh-speed rocker arm 12 c (not shown), and these arms are pivotedtogether. As a result, with rotation of the camshaft 10, the low-speedand inactive rocker arms 12 a, 12 b are driven via the high-speed rockerarm 12 c by the high-speed cam 11 c having the highest cam nose wherebyboth the first and second intake valves IV1, IV2 are opened and closedby a high-speed valve timing (hereinafter referred to as “Hi. V/T”)corresponding to the cam profile of the high-speed cam 11 c.Hereinafter, such an operation mode of the two intake valves IV1, IV2 bythe VTEC 13 is referred to as “the HI. V/T mode” as required. In the Hi.V/T mode, both the first and second intake valves IV1, IV2 are openedand closed by a large lift, whereby the intake air amount is increasedto deliver a larger power output.

Further, the cam-type valve actuating mechanism 6 for actuating thefirst and second exhaust valves EV1, EV2 is comprised of an exhaustcamshaft 24, exhaust cams 25 a, 25 b fitted on the exhaust camshaft 24,exhaust rocker arms (not shown), and so forth, as shown in FIG. 1. Theexhaust valves EV1, EV2 are opened and closed by valve lifts and inopening and closing timing corresponding to the cam profiles of theexhaust cams 25 a, 25 b. It should be noted that the cam-type valveactuating mechanism 6 may be also configured to be provided with a camprofile-switching mechanism to thereby switch the first and secondexhaust valves EV1, EV2 between low-speed valve timing and high-speedvalve timing.

The variable valve-closing timing device 7 includes a rocker arm 26(holding rocker arm) for an electromagnetic actuator 29, referred tohereinafter, which is located adjacent to the low-speed rocker arm 12 aand pivotally mounted on the rocker shaft 14. As shown in FIG. 4, thisrocker arm (hereinafter referred to as “the EMA rocker arm”) 26protrudes farther outward than the low-speed and inactive rocker arms 12a, 12 b. The variable valve-closing timing device 7 further includes asecond switching valve 27 (switching mechanism) for hydraulicallyswitching between the connection and disconnection of the EMA rocker arm26 and the low-speed rocker arm 12 a, and a second oilpressure-switching mechanism (switching mechanism) for switching betweenthe supply and cut-off of oil pressure to the second switching valve 27,an electromagnetic actuator 29 for making blocking or latchingengagement, via the EMA rocker arm 26 and the low-speed rocker arm 12 a,with the first intake valve which has been opened, to hold the same, ahydraulic impact-lessening mechanism 30 for lessening an impact on thefirst intake valve IV1 which is caused by operation of theelectromagnetic actuator 29, and a lost-motion spring 26 a forpreventing the EMA rocker arm 26 from pivotally moving downward by afollow-up spring 41, referred to hereinafter, of the electromagneticactuator 29, when the EMA rocker arm 26 and the low-speed rocker arm 12a are disconnected from each other.

As shown in FIG. 4, the second switching valve 27 is formed by a pistonvalve, similarly to the first switching valve 17 of the VTEC 13, andincludes pistons 31 a, 31 b slidably arranged for the low-speed and EMArocker arms 12 a, 26 and in axial abutment with each other, an oilchamber 32 formed in the piston 31 a, and a coil spring 33 arrangedbetween the piston 31 b and the EMA rocker arm 26, for urging the piston31 b toward the low-speed rocker arm 12 a. The oil chamber 32 iscommunicated with the second oil pressure-switching mechanism 28 via anoil passage 34 formed through the low-speed rocker arm 12 a and thesecond oil passage 16 b formed through the rocker shaft 14. The secondoil pressure-switching mechanism 28 is, similarly to the first oilpressure-switching mechanism 18 of the VTEC 13, comprised of anelectromagnetic valve and a spool (none of which is shown), andconnected to an oil pump (not shown). The second oil pressure-switchingmechanism 28 is driven by a control signal from the ECU 2, for switchingbetween the supply and cut-off of the oil pressure to the secondswitching valve 27 via the second oil passage 6 b, etc.

Therefore, during interruption of the supply of oil pressure from thesecond oil pressure-switching mechanism 28 to the second switching valve27, the pistons 31 a, 31 b of the second switching valve 27 are held inrespective positions shown in FIG. 4 by the urging force of the coilspring 33, in which the pistons 31 a, 31 b are engaged with thelow-speed and EMA rocker arms 12 a, 26 alone, respectively, whereby thetwo rocker arms 12 a, 26 are disconnected from each other and pivotedindependently of each other. On the other hand, although not shown, whenthe oil pressure is supplied from the second oil pressure-switchingmechanism 28 to the oil chamber 32 of the second switching mechanism 27,the pistons 31 a, 31 b are slid toward the coil spring 33 against theurging force thereof, so that the piston 31 b is engaged with thelow-speed and EMA rocker arms 12 a, 26 in a bridging fashion, wherebythe two rocker arms 12 a, 26 are connected with each other, and pivotedtogether.

As shown in FIG. 5, the electromagnetic actuator (hereinafter referredto as “the EMA”) 29 as an actuator is comprised of a casing 35, anelectromagnet 38 formed by a yoke 36 and a coil 37 received in a lowerspace within the casing 35, an armature 39 received above them, astopper rod 40 (stopper) integrally formed with the armature 39 andextending downward through the electromagnet 38 and the casing 35 to theEMA rocker arm 26, and the follow-up coil spring 41 for urging thearmature 39 downward such that the armature 39 follows motion of the EMArocker arm 26. The coil 37 is connected to the ECU 2, and itsenergization is controlled by the ECU 2.

It should be noted that, as shown in FIGS. 3 and 4, an abutment portion29 a of the EMA rocker arm 26 with which the stopper 40 of the EMA 29abuts is disposed at a location remoter from the rocker shaft 14 than anabutment portion 12 d of the low-speed rocker arm 12 a with which thefirst intake valve IV1 abuts. This configuration makes it possible toreduce the holing force required of the EMA 29 for holding the firstintake valve IV1, thereby enabling reduction of the size of the EMA 29and saving of energy. Further, since the EMA rocker arm 26 is a separatemember from the low-speed rocker arm 12 a, even if the abutment portion12 d is disposed as described above, it is possible to avoid an increasein the size of the low-speed rocker arm 12 a, and the resulting increasein the inertial mass in an inactive mode of the EMA 26. Further, as theabutment portion 29 a is disposed remoter from the rocker shaft 14 thanthe abutment portion 12 d, the holding force of the EMA 29 can be madesmaller, and as a result, the size of EMA 29 can be reduced.

According to the above configuration, when the ordinary valve-openingand closing operation by the camshaft 10, the second switching valve 27disconnects between the low-speed and EMA rocker arms 12 a, 26, so thatthe armature 39 and the stopper rod 40 press the EMA rocker arm 26 in avalve-lifting (valve-opening) direction (downward as viewed in FIG. 3)by the urging force of the follow-up coil 41. In this case, the EMArocker arm 26 is held on a base circle of the camshaft 10 (in a statenot lifting the first intake valve IV1), by the lost-motion spring 26set to the larger spring force than that of the follow-up coil spring41, whereby the EMA rocker arm 26 is held in a state connectable withthe low-speed rocker arm 12 a. As a result, the base circle of thecamshaft 10 serves as a stopper, and restricts further motion of the EMArocker arm 26, which prevents a larger urging force than required fromacting on the EMA 29 and the hydraulic impact-lessening mechanism 30, sothat durability of the EMA 29 and the hydraulic impact-lesseningmechanism 30 can be improved.

On the other hand, when operating conditions set by the ECU 2 aresatisfied, to attain the optimum valve-closing timing for the operatingconditions, the second switching valve 27 is operated by the second oilpressure-switching mechanism 28, whereby the EMA rocker arm 26 isconnected to the low-speed rocker arm 12 a on the base circle of thecamshaft 10. In this state, when the valve-opening and closing operationby the intake cam 11 is started, when the first intake valve IV1 ismoving in the valve-lifting direction, the EMA rocker arm 26 is drivendownward by the intake cam 11 against the urging force of thelost-motion spring 26 a, and accordingly, the armature 39 and thestopper rod 40 are lifted by the follow-up coil spring 41 in a fashionfollowing the EMA rocker arm 26. Further, in parallel with this, thecoil 37 is energized in appropriate timing to magnetize the yoke 36.Then, immediately before the first intake valve IV1 reaches the maximumlift (e.g. 0.01 to 0.85 mm), the armature 39 is seated on the yoke 36(CRK1 in FIG. 6), and thereafter, the EMA rocker arm 26 leaves thestopper rod 40. Then, by the time the first intake valve IV1 is broughtinto abutment with the stopper rod 40 again after reaching the maximumlift (CRK3 in FIG. 6), the magnetized state of the yoke 36 isestablished (CRK2 in FIG. 6), so that the armature 39 maintains a stateseated on the yoke 36 by the holding force of the yoke 36 whichovercomes the urging force of the coil spring 3 c of the first intakevalve IV1. As a result, the first intake valve IV1 is brought intoblocking (or catching) engagement with the stopper rod 40 via thelow-speed rocker arm 12 a and the EMA rocker arm 26, and held in an openstate by a predetermined lift (hereinafter referred to as “the holdinglift”) VLL corresponding to a protruded position of the stopper rod 40.

Further, thereafter, when the holding of the first intake valve IV1 bythe EMA 29 is canceled by stopping the energization of the coil 37 andthereby demagnetizing the yoke 36, the first intake valve IV1 is closedby the urging force of the coil spring 3 c. Therefore, the operation ofthe EMA 29 makes it possible not only to close the first intake valveIV1 later than when the first intake valve IV1 is actuated by the intakecam 11, and but also to control the closing timing of the first intakevalve IV1 as desired by controlling the timing of turning-off of thecoil 37.

The hydraulic impact-lessening mechanism 30 lessens the impact appliedwhen the first intake valve IV1 is closed upon cancellation of theholding of the same by the EMA 29. As shown in FIGS. 3 and 4, thehydraulic impact-lessening mechanism 30 is comprised of a casing 30 adefining an oil chamber 30 b therein, a piston 30 c horizontallyslidably inserted into the oil chamber 30 b with one end protruding outfrom the casing 30 a, a valve chamber 30 d arranged within the oilchamber 30 b and formed with a port 30 e on a side remote from thepiston 30 c, a ball 30 f received within the valve chamber 30 d, foropening and closing the port 30 e, and a coil spring 30 g arrangedbetween the ball 30 f and the piston 30 c, for urging the piston 30 coutward. The piston 30 c is in abutment with an upward-extending portionof the EMA rocker arm 26 on an opposite side to the abutment portion 29a with which the stopper rod 40 of the EMA 29 abuts.

According to the configuration described above, the hydraulicimpact-lessening mechanism 30 is in a state shown in FIG. 3 when theintake valve IV1 is closed, that is, since the EMA rocker arm 26 hasbeen pivoted in an anticlockwise direction as viewed in the figure, thepiston 30 c is positioned leftward, whereby the coil spring 30 g iscompressed, and the ball 30 f closes the port 30 e. From this state,when the intake valve IV1 is moved in the valve-opening direction, theEMA rocker arm 26 is pivoted in a clockwise direction, whereby thepiston 30 c is slid rightward. In accordance therewith, the ball 30 fopens the port 30 e to allow oil to fill the valve chamber 30 d, and thecoil spring 30 g is expanded. Then, when the first intake valve IV1 ismoved in the valve-closing direction after cancellation of the holdingthereof by the EMA 29, the EMA rocker arm 26 is braked by the urgingforce of the coil spring 30 g and the oil pressure, whereby the impacton the first intake valve IV1 is lessened.

On the other hand, a crankshaft angle sensor 42 (operatingcondition-detecting means) is arranged around the crankshaft. Thecrankshaft angle sensor 42 delvers a CYL signal, a TDC signal, and a CRKsignal, as pulse signals, at respective predetermined crank anglepositions to deliver the same to the ECU 2. The CYL signal is generatedat a predetermined crank angle position of a particular cylinder. TheTDC signal indicates that the piston (not shown) of each cylinder 4 isat a predetermined crank angle position in the vicinity of the TDC (topdead center) position at the start of the intake stroke of the piston,and in the case of the four-cylinder engine of the present embodiment,one pulse of the TDC signal is delivered whenever the crankshaft rotatesthrough 180 degrees. Further, the CRK signal is generated at a shortercycle than that of the TDC signal i.e. whenever the crankshaft rotatesthrough e.g. 30 degrees. The ECU 2 determines the respective crank anglepositions of the cylinders on a cylinder-by-cylinder basis, based onthese CYL, TDC, and CRK signals, and calculates the rotational speed(hereinafter referred to as “the engine rotational speed”) Ne based onthe CRK signal.

Further input to the ECU 2 are a signal indicative of an acceleratoropening ACC which is a stepped-on amount of an accelerator pedal (notshown) from an accelerator opening sensor 43 (operatingcondition-detecting means) and a signal indicative of a valve lift VL ofthe first intake valve IV1 from a lift sensor 44.

Now, the operations of the valve control apparatus 1 describedheretofore will be described collectively with reference to FIG. 6. Thisfigure shows an example of a case in which the first intake valve IV1and the second intake valve IV2 are opened and closed in Lo. V/T andinactive V/T, respectively. As shown in the figure, the first and secondexhaust valves EV1, EV2 are actuated by following the respective camprofiles of the exhaust cams 25 a, 25 b, whereby they start to open at acrank angle position slightly before their BDC before the exhaust strokeand terminate closing slightly after their TDC before the intake stroke.The second intake valve IV2 is opened by the inactive cam 11 a followingits cam profile by a very small lift during an end portion of the intakestroke.

Further, the intake valve IV1 is actuated by the low-speed cam 11 afollowing its cam profile, thereby starting to open slightly before theTDC before the intake stroke, and when the EMA 29 is inactive,terminates its closing operation slightly after its BDC before thecompression stroke (hereinafter after referred to as “BDC closing”). Onthe other hand, when the EMA 29 is active, the coil 37 starts to beenergized in timing before the lift VL of the first intake valve IV1reaches the aforementioned holding lift VLL. This energization starttiming is made earlier as the engine rotational speed NE is higher, soas to enable time to be secured which is necessary for operation of theEMA 29. For example, the latest timing is set to approximately the sametiming as the armature 39 is seated (CRK1 in FIG. 6) and the earliesttiming is set to timing (CRK0 in FIG. 6) earlier than the TDC. Thisestablishes the magnetized state of the yoke 36 in a predeterminedtiming after the armature 39 of the EMA 29 is seated on the yoke 36(CRK2). In the meanwhile, the lift VL of the first intake valve IV1undergoes changes following the cam profile of the low-speed cam 11 a,and when it is equal to the holding lift VLL after passing the maximumlift, the EMA rocker arm 26 is brought into blocking engagement with thestopper rod 40, whereby it is held at the holding lift VLL (CRK3).

Thereafter, until the energization of the coil 37 is stopped, the liftVL of the first intake valve IV1 is held at the holding lift VLL, sothat the low-speed cam 11 a is moved away from the low-speed rocker arm12 a and freely rotates. Then, the coil 37 is turned off (e.g. CRK4) todecrease the magnetic force acting on the armature 39, whereby the firstintake valve IV1 is liberated from the holding by the EMA 29 (CRK5), andis moved by the spring force of the coil spring 3 c along the valve liftcurve VLDLY1 to the valve-closing position. After that, at a crank angleposition (CRK6) slightly before the valve-closing position, thehydraulic impact-lessening mechanism 30 starts to act to therebydecelerate the first intake valve IV1, which finally reaches thevalve-closing position in a cushioned state (CRK7).

It should be noted that the valve lift curve VLDLY1 mentioned aboverepresents a case of the coil 37 being turned off latest, and a valvelift curve VLDLY2 in FIG. 6 represents a case of the coil 37 beingturned off earliest. That is, the hatched area enclosed by the two valvelift curves VLDLY1, VLDLY2 represents a late closing region of the firstintake valve IV1 in which the late closing can be carried out by thevariable valve-closing timing device 7. Thus, by controlling the timingin which the coil 37 is turned off, the closing timing of the firstintake valve IV1 can be controlled as desired within this late closingregion.

The ECU 2 in the present embodiment forms control means, operatingcondition-detecting means, and operation mode-determining means, and isimplemented by a microcomputer comprised of a CPU, a RAM, a ROM, and aninput/output interface (none of which is shown). The above-mentionedsignals indicative of detections by the sensors 42 to 44 are input tothe CPU after A/D conversion and shaping by the input/output interface.The CPU determines operating conditions of the engine 3 by controlprograms stored in the ROM according to these input signals, andcontrols the operations of the variable valve-closing timing device 7and the VTEC 13 in the following manner:

FIGS. 7 and 8 shows a flowchart of a valve control process which isexecuted by the ECU 2 whenever the TDC signal pulse is generated. Inthis valve control process, first in a step 61 (in the figures, shown as“S61”, which rule applies similarly in the following description), it isdetermined whether or not a fail has occurred on the EMA 29. Thisdetermination is carried out e.g. based on the lift VL of the firstintake valve IV1 detected by the lift sensor 44. More specifically, whenthe EMA 29 is to be operated, if the lift VL is not held at the holdinglift VLL, judging that the EMA 29 is in an inoperative state, or whenthe lift VL continues to be held at the holding lift VLL for more than apredetermined time period, judging that the stopper rod 40 of the EMA 29is in a state incapable of returning to a withdrawn position(inactivation incapable state), it is determined that a fail hasoccurred on the EMA 29.

If the answer to the question of the step 61 is negative (NO), i.e. ifno fail has occurred on the EMA 29, it is determined whether or not theengine 3 is in a start mode (step 62). This determination is carried oute.g. based on the engine rotational speed Ne, and when the enginerotational speed Ne is equal to or lower than a predetermined rotationalspeed (e.g. 500 rpm), it is determined that the engine is in the startmode. If the answer to this question is affirmative (YES), and hence theengine 3 is in the start mode, the valve timing of the first intakevalve IV1 and that of the second intake valve IV2 are set to Lo. V/T andinactive V/T, respectively, by the VTEC 13 (step 63), and the EMA 29 isset to the inactive mode (step 64). That is, when the engine 3 is in thestart mode, the EMA 29 is made inactive.

On the other hand, if the answer to the question of the step 62 isnegative (NO), i.e. if the engine 3 is not in the start mode, it isdetermined whether or not the engine 3 is in an operating region A (step65). FIG. 9 shows an example of a map defining operating regions of theengine 3. The operating region A corresponds to an idle operating regionin which the engine rotational speed Ne is lower than a firstpredetermined value N1 (e.g. 800 rpm) and the accelerator opening ACC islower than a first predetermined value AC1 (e.g. 10%), an operatingregion B corresponds to a low-rotational speed/low-load region in whichthe Ne value is lower than a second predetermined value N2 (e.g. 3500rpm) and the ACC value is lower than a second predetermined value AC2(e.g. 80%), exclusive of the operating region A, an operating region Ccorresponds to a low-rotational speed/high-load region in which the Nevalue is lower than the second predetermined value N2 and the ACC valueis equal to or higher than the second predetermined value AC2, and anoperating region D correspond to a high-rotational speed region in whichthe Ne value is equal to or higher than the second predetermined valueN2.

If the answer to the question of the step 65 is affirmative (YES) andhence the engine 3 is in the operating region A (idle operating region),similarly to the case of the engine 3 being in the start mode, the firstand second intake valves IV1, IV2 are set to Lo. V/T and inactive V/T,respectively (step 66) and the EMA 29 is set to the inactive mode (step67).

If the answer to the question of the step 65 is negative (NO), it isdetermined whether or not the engine 3 is in the operating region B(step 68). If the answer to this question is affirmative (YES), thefirst and second intake valves IV1, IV2 are set to Lo. V/T and inactiveV/T (step 69), similarly to the case of the engine 3 being in the idleoperating region, whereas the EMA 29 is set to the active mode (step70). In other words, when the engine 3 is in the low-rotationalspeed/low-load region, the EMA 29 is made active whereby the firstintake valve IV1 is controlled to late closing. This makes it possibleto retard the closing timing of the first intake valve IV1, therebyreducing pumping loss and improving fuel economy.

If the answer to the question of the step S68 is negative (NO), it isdetermined whether or not the engine 3 is in the operating region C(step 71). If the answer to the question is affirmative (YES), the firstand second intake valves IV1, IV2 are set to Lo. V/T and inactive V/T,respectively (step 72), whereas the EMA 29 is set to the inactive mode(step 73). In other words, when the engine is in the low-rotationalspeed/high-load region, the EMA 29 is made inactive, whereby the closingtiming of the first intake valve IV1 is set to the BDC closing by thelow-speed cam 11 a, whereby the actual stroke volume can be increased toincrease the power output.

If the answer to the question of the step S71 is negative (NO), i.e. ifthe engine 3 is in the operating region D, the first and second intakevalves IV1, IV2 are both set to Hi. V/T (step 74) and the EMA 29 is setto the inactive mode (step 75). In other words, when the engine is inthe high-rotational speed region, the first and second intake valvesIV1, IV2 are set to Hi. V/T, whereby the lift is increased to increasethe amount of intake air, and the closing timing of the first intakevalve IV1 is set to the BDC closing to increase the actual strokevolume, which makes it possible to increase the power output to themaximum.

On the other hand, if the answer to the question of the step S61 isaffirmative (YES), i.e. if a fail has occurred on the EMA 29, theprogram proceeds to a step 77 in FIG. 8, wherein it is determinedwhether or not the engine 3 is in an operating region E. FIG. 10 shows atable defining an example of operating regions of the engine applied tothe valve control process when a fail has occurred, in which theoperating region E corresponds to a low-rotational speed region in whichthe engine rotational speed Ne is lower than a third predetermined valueN3 (e.g. 3500 rpm), and an operating region F correspond to ahigh-rotational speed region in which the Ne value is equal to or higherthan the third predetermined value N3.

If the answer to the question of the step S77 is affirmative (YES), andhence the engine 3 is in the operating region E (low-rotational speedregion), the first and second intake valves IV1, IV2 are set to Lo. V/Tand inactive V/T, respectively (step 78), and the EMA 29 is set to theinactive mode (step S79). On the other hand, if the answer to thequestion of the step S77 is negative (NO), and hence the engine 3 is inthe operating region F, the first and second intake valves IV1, IV2 areboth set to Hi. V/T (step 80), and the EMA 29 is set to the inactivemode (step 81). As described above, when a fail has occurred on the EMA29, the EMA 29 is made inactive, whereby the fail of the EMA 29 isprevented from causing adverse effects on the operations of the firstand second intake valves IV1, IV2, and the valve timing of these valvesis switched depending on the rotational speed region of the engine 3,whereby the first and second intake valves IV1, IV2 can be actuated bythe cam-type valve actuating mechanism 5 without any trouble.

Referring again to FIG. 7, in a step 76 following the step 64, 67, 70,73, 75, 79, or 81, a control process for the EMA 29 (hereinafterreferred to as “the EMA control process”) is carried out. In the EMAcontrol process, according to the active mode of the EMA 29 set in thestep S64, 67, 70, 73, 75, 79, or 81, whether the EMA 29 is to be madeactive or inactive is determined, and when the EMA 29 is to be madeactive, the energization of the respective coils 37 of the respectiveEMAs (EMA1 to EMA4) of the four cylinders 4 is controlled.

FIG. 11 shows a subroutine of the EMA control process. In this process,first, it is determined whether or not the operation mode of the EMA 29has been set to the active mode (step 101). If the answer to thisquestion is negative (NO), and hence the EMA 29 has been set to theinactive mode, a power supply to a drive circuit (none of which isshown) for supplying electric current to the coil 37 of the EMA 29 andthe second oil pressure-switching mechanism 28 is turned off (step 102),followed by terminating the present program. This makes the EMA 29inactive by stopping energization of the coil 37 when the EMA 29 hasbeen set to the inactive mode. Further, in this case, even if the EMA 29cannot be made inactive by stopping energization of the coil 37 due to afail having occurred on the EMA 29 itself, the low-speed rocker arm 12 ais made free from the EMA rocker arm 26 by stopping supply of electriccurrent to the second oil pressure-switching mechanism 28, therebystopping the second switching valve 27 from operating. As a result, theEMA 29 is no longer connected with the first intake valve IV1, and henceincapable of holding the same. This enables the first intake valve IV1to be actuated by the cam-type valve actuating mechanism 5 without anytrouble while positively preventing the fail of the EMA 29 from causingadverse effects on the operation of the first intake valve IV1.

On the other hand if the answer to the question of the step 101 isaffirmative (YES), and hence the EMA 29 has been set to the active mode,the power supply to the drive circuit is turned on (step 103), wherebythe coil 37 is made energizable, and by driving the second oilpressure-switching mechanism 28, the second switching valve 27 isoperated, whereby the low-speed rocker arm 12 a and the EMA rocker arm26 are connected to each other.

Next, it is determined whether or not the EMA1 is in timing for startingenergization (step 104), and when the answer to this question becomesaffirmative (YES), the EMA1 starts to be energized (step 105). Thetiming for starting the energization is set according to the enginerotational speed Ne, as described hereinabove. If the answer to thequestion of the step 104 is negative (NO), it is determined whether ornot the EMA1 is in timing for terminating the energization (step 106).When the answer to this question becomes affirmative (YES), theenergization of the EMA1 is terminated (step 107). The timing fortermination of the energization is set according to the enginerotational speed Ne and the accelerator opening ACC, as describedhereinbelow.

Thereafter, similarly to the above, in steps 108 to 111, steps 112 to115, and steps 116 to 119, the start and termination of the energizationof the EMA2 to EMA4 are controlled, respectively, followed byterminating the program.

FIG. 12 shows an example of the closing timing of the first intake valveIV1 under the low rotational speed condition (e.g. 1500 rpm). As shownin the figure, the closing timing of the first intake valve IV1 isbasically set to later timing as the load on the engine represented bythe accelerator opening ACC is lower, and for example, when theaccelerator opening ACC is around 20%, the intake valve IV1 is set tovery late closing timing of about BDC+130 degrees. This can minimize thepumping loss in the low-rotational speed/low-load region in which theengine is frequently operated, whereby the improvement in fuel economycan be made maximum. Further, the valve-closing timing is configuredsuch that as the load increases, it progressively approaches the BDC,whereby the power output can be increased. It should be noted that theregion for late closing is narrowed for the very small load condition inorder to cope with the problem of combustion fluctuation by making thevalve-closing timing earlier, since the combustion fluctuation tends tostart to occur when the engine is under the very low load condition.

As described above, according to the valve control apparatus of thepresent embodiment, the cam-type valve actuating mechanism 5 actuatesthe first and second intake valves IV1, IV2, and the EMA 29 is operatedas required, whereby the closing timing of the first intake valve IV1can be controlled as desired. This makes it possible to attain themaximum fuel economy and power output in a manner adapted to anyoperating conditions of the engine. That is, as described above, in thelow-rotational speed/low-load operating region, the closing timing ofthe first intake valve IV1 is controlled to late closing in a manneradapted to each of possible cases of the operating conditions of theengine 3, whereby the pumping loss can be minimized, and hence the fueleconomy can be largely improved. Further, in the high-rotationalspeed/high-load region, the EMA 29 is made inactive, and the firstintake valve IV1 is actuated by the cam-type valve actuating mechanism 5alone, whereby higher rotational speed and higher power output can berealized without being affected by the follow-up capability of the EMA29.

Further, the first intake valve IV1 is basically actuated by thecam-type valve actuating mechanism 5, and the EMA 29 is only required toblock the first intake valve IV1 by one electromagnet 38 in onedirection, and hence one electromagnet 38 is sufficient for one cylinder4, which allows reduction of weight and cost of the apparatus. Further,since the EMA 29 is operated only when the operating conditions thereofare satisfied, this merit and the use of one electromagnet 38 make itpossible to reduce the electric power consumption, and further improvethe fuel economy by the reduction of the electric power consumption.

Moreover, since the first intake valve IV1 can be operated by thecam-type valve actuating mechanism 5 alone, even when a fail, such asloss of synchronization, has occurred on the EMA 29, the first intakevalve IV1 can be actuated by the cam-type valve actuating mechanism 5without any trouble. Further, even if the EMA 29 cannot be made inactivedue to the fail, it is possible to forcibly make the EMA 29 incapable ofmaking blocking engagement with the first intake valve IV1, by stoppingthe supply of current to the second oil pressure-switching mechanism 28.Therefore, it is possible to positively prevent the fail of the EMA 29from adversely affecting the first intake valve IV1, and preventdegradation of combustion state and resulting increase in exhaustemissions.

Further, at the start of the engine 3 during which it takes time toincrease oil pressure, the EMA 29 is made inactive, and the first intakevalve IV1 is actuated by the cam-type valve actuating mechanism 5 alone,which ensures the stable operation of the first intake valve IV1.

Further, the hydraulic impact-lessening mechanism 30 lessens the impactreceived by the first intake valve IV1 when it returns to thevalve-closing position after cancellation of the holding thereof by theEMA 29, and noise caused by the impact can be suppressed. In this case,when the hydraulic oil is in a very low temperature condition or hightemperature condition in which the viscosity of the hydraulic oil isliable to change and hence the impact-lessening performance may not bemaintained, the EMA 29 is made inactive to thereby fully ensure theimpact-lessening performance of the mechanism 30.

FIGS. 13 and 14 show a valve control apparatus according to a secondembodiment of the invention. This embodiment is distinguished from thefirst embodiment in which the EMA rocker arm 26 is used, in that the EMArocker arm 26 is removed, but the EMA 29 is caused to directly act onthe low-speed rocker arm 12 a. In accordance with the removal of the EMArocker arm 26, the second switching valve 27 and the second oilpressure-switching mechanism 28 for causing the EMA rocker arm 26 to beconnected with the low-speed rocker arm 12 a are also removed, and therocker shaft 14 is formed with only the first oil passage 16 for theVTEC 13. Further, the hydraulic impact-lessening mechanism 30 has itspiston 30 c in abutment with the low-speed rocker arm 12 a, and theimpact on the first intake valve IV1 is lessened via the low-speedrocker arm 12 a. Further, the EMA 29 has an hydraulic inactivatingmechanism 45 (switching mechanism) attached thereto, for making the EMA29 inactive. The hydraulic inactivating mechanism 45 is controlled bythe ECU 2, and is configured to hydraulically lock the stopper rod 40during operation thereof, and the other features of the arrangement ofthe apparatus is the same as those of the first embodiment.

Therefore, in the present embodiment as well, the operation modes of thefirst and second intake valves IV1, IV2 can be switched between theLo.-inactive V/T mode and the Hi. V/T mode, and by causing the EMA 29 todirectly make blocking engagement with the low-speed rocker arm 12 a,the closing timing of the first intake valve IV1 can be changed asdesired. Therefore, the same effects of the first embodiment describedabove can be obtained. Further, when a fail has occurred on the EMA 29,the hydraulic inactivating mechanism 45 is operated, whereby the EMA 29can be forcibly made inactive, so that the first intake valve IV1 can beactuated by the cam-type valve actuating mechanism 5 without anytrouble. The present embodiment is particularly advantageous in the casewhere the EMA rocker arm cannot be added to the cam-type valve actuatingmechanism 5 due to the layout or other constraints.

FIG. 15 shows a valve control apparatus according to a third embodimentof the invention. This embodiment is distinguished from the firstembodiment in construction of the VTEC 13, i.e. in that the VTEC 13 ofthe present embodiment includes a third switching valve 46 for switchingbetween the connection and disconnection of the low-speed rocker arm 12a and the inactive rocker arm 12 b, in addition to the first switchingvalve 17, whereby it is configured that the first and second intakevalves IV1, IV2 can be simultaneously opened and closed in Lo. V/T.

The third switching valve 46 basically has the same construction as thefirst switching valve 17, that is, it includes pistons 47 a, 47 bslidably provided for the low-speed and inactive rocker arms 12 a, 12 b,an oil chamber 48 formed in a piston 47 b, and a coil spring 49 forurging the piston 47 a toward the inactive rocker arm 12 b. The oilchamber 48 is communicated with the third oil pressure-switchingmechanism (not shown) via an oil passage 50 formed through the inactiverocker arm 12 b and a third oil passage 16 c formed through the rockershaft 14. This third oil pressure-switching mechanism is controlled bythe ECU 2, whereby the supply and cut-off of the oil pressure to thethird switching valve 46 is switched.

According to the configuration described above, when the third switchingvalve 46 is not supplied with oil pressure, the pistons 47 a, 47 b areengaged with the low-speed and inactive rocker arms 12 a, 12 b alone,respectively, by the urging force of the coil spring 49, whereby the tworocker arms 12 a, 12 b are disconnected from each other and in a freestate (state shown in FIG. 15). Therefore, in this state, the firstswitching valve 17 can switch the operation of the first and secondintake valves IV1, IV2 between the Lo.-inactive V/T mode and the Hi. V/Tmode. On the other hand, when the supply of oil pressure to the firstswitching valve 17 is stopped and the third switching valve 46 issupplied with oil pressure, the piston 47 b is engaged with thelow-speed and inactive rocker arms 12 a, 12 b in a bridging manner,whereby the rocker arms 12 a, 12 b are connected with each other tooperate together, so that the first and second intake valves IV1, IV2are both opened and closed by the low-speed cam 11 a in Lo. V/T(hereinafter referred to as “the Lo. V/T mode”). Further, in this Lo.V/T mode, by supplying the oil pressure to the second switching valve 27to cause the EMA 29 to operate, the closing timing of the first andsecond intake valves IV1, IV2 can be simultaneously controlled.

As described above, in the present embodiment, the respective operationmodes of the first and second intake valves IV1, IV2 can be switchedbetween the three modes of the Lo.-inactive V/T mode, the Hi. V/T mode,and the Lo. V/T mode. Further, in the Lo.-inactive V/T mode, the closingtiming of the first intake valve IV1 can be controlled, while in the Lo.V/T mode, the closing timing of the first and second intake valves LV1,LV2 can be simultaneously controlled.

FIG. 16 shows a summary of examples of operation settings of the firstand second intake valves IV1, IV2 and the EMA 29 for operating regionsof the engine 3. FIG. 17 shows an example of a map of the operatingregions. In this operating region map, the operating region D appearingin FIG. 9 is subdivided into smaller regions, and within this operatingregion D, a region in which the engine rotational speed Ne is lower thana fourth predetermined value N4 (e.g. 4500 rpm) and the acceleratoropening ACC is lower than the second predetermined value AC2 is set toan operating region D1 (medium-rotational speed/low-load region), aregion in which the Ne value is lower than the fourth predeterminedvalue N4 and the ACC value is equal to or higher than the secondpredetermined value AC2 is set to an operating region D2(medium-rotational speed/high-load region), and a region in which the Nevalue is equal to higher than the fourth predetermined value N4 is setto an operating region D3.

Then, as shown in FIG. 16, in the operating region D1, the first andsecond intake valves IV1, IV2 are both set to Lo. V/T and the EMA 29 ismade active whereby both the intake valves IV1, IV2 are controlled tolate closing. Further, in the operating region D2, the intake valvesIV1, IV2 are set to Lo. V/T and at the same time, the EMA 29 is madeinactive, and in the operating region D3, the intake valves IV1, IV2 areset to Hi. V/T, and the EMA 29 is made inactive. The operation settingsin the other operating regions are the same as those in the firstembodiment.

Therefore, in the present embodiment, it is possible to obtain the sameadvantageous effects as provided by the first and second embodiments,and in addition, in the operating region D1, i.e. in themedium-rotational speed/low-load region, the first and second intakevalves IV1, IV2 are controlled to late closing, which makes it possibleto widen the region in which the pumping loss is reduced, and therefore,it is possible to further improve the fuel economy.

FIG. 18 shows a variation of the valve control apparatus. As is clearfrom comparison with FIG. 15, this variation is distinguished from thevalve control apparatus of the third embodiment in that the constructionof the EMA rocker arm 26 is modified. The EMA rocker arm 26 is formed tohave an L shape bent away from the low-speed rocker arm 12 a, and theabutment portion 29 b of the EMA rocker arm 26 with which the stopperrod 40 of the EMA 29 abuts is disposed at a location closer to therocker shaft 14 than the abutment portion 12 d of the low-speed rockerarm 12 a with which the first intake valve IV1 abuts. Therefore,according to this variation, it is possible to reduce the stroke of theactuator required to hold the first intake valve IV1, whereby the lengthof the stopper rod 4 can be reduced to reduce the size of the apparatusalong the axis of the stopper rod 4, and further, since the abutmentportion 29 b is disposed closer to the rocker shaft 14, the distancefrom the rocker shaft 14 to the abutment portion 12 d of the low-speedrocker arm 12 a with which the first intake valve IV1 abuts can bereduced, which makes it possible to reduce the size of the apparatus inthis direction. Thus, the valve system can be reduced in size in boththe directions. Further, since the EMA rocker arm 26 is a separatemember from the low-speed rocker 12 a, even if the abutment portion 29 bis arranged as described above, interference with the first oilpressure-switching mechanism 18 and so forth arranged in its vicinitycan be avoided. Therefore, the EMA 29 can be disposed in compactarrangement in the direction of operation of the stopper rod 40.

FIG. 19 shows a valve control apparatus according to a fourth embodimentof the invention. This embodiment is distinguished from the first tothird embodiment in the construction of the EMA 29. This EMA 29 includesa pair of upper and lower electromagnets 38 a, 38 b, and an armature 39integrally formed with the stopper rod 40 is disposed between theseelectromagnets 38 a, 38 b. The stopper rod 40 is urged downward by thefollow-up coil spring 41, and at the same time, connected to the EMArocker arm 26 to operate together. Further, as shown in FIG. 20, thestroke of the EMA 29 is configured such that it is larger than themaximum lift of the first intake valve IV1 in Lo. V/T, and at the sametime, smaller than the maximum lift of the same in Hi. V/T.

Therefore, according to this construction, in the active mode of the EMA29 in which the EMA rocker arm 26 is connected to the low-speed rockerarm 12 a, by controlling the timing of energization of the upper andlower electromagnets 38, it is possible to control the opening andclosing timing of the first intake valve IV1. More specifically, asindicated by a hatched area in FIG. 20, it is possible not only tocontrol the first intake valve IV1 to late closing similarly to thefirst to third embodiments but also to control the same to earlyopening. Further, since the stroke of the EMA 29 is larger than themaximum lift of the first intake valve IV1 in Lo. V/T, it is possible tocarry out early opening of the first intake valve IV1 in Lo. V/T, andcontinue the state, whereby even the preferential application of thevalve timing by the EMA 29 to Lo. V/T is also possible. It should benoted that in the inactive mode of the EMA 29 in which the EMA rockerarm 26 is disconnected from the low-speed rocker arm 12 a, similarly tothe embodiments described above, the low-speed rocker arm 12 a ispivoted in a state completely free from them the EMA rocker arm 26 andthe EMA 29 without being adversely affected by the intertial massthereof.

FIG. 21 shows an example of operation settings of the first and secondintake valves IV1, IV2 and the EMA 29 in the present embodiment foroperating regions of the engine 3. FIG. 22 shows an example of a map ofthese operating regions. As shown in these figures, in this example, inan operating region G (low-rotational speed/low-load region) in whichthe engine rotational speed Ne is lower than a fifth predetermined valueN5 (e.g. 800 rpm) and at the same time the accelerator opening ACC islower than a third predetermined value AC3 (e.g. 10%), the first intakevalve IV1 and the second intake valve IV2 are set to Lo. V/T andinactive V/T, respectively, and the EMA 29 is made inactive. Further, anoperating region H (medium-rotational speed/low-load region) in whichthe Ne value is equal to or higher than the fifth predetermined value N5and lower than a sixth predetermined value N6 (e.g. 3500 rpm) and theACC value is lower than a fourth predetermined value AC4 (e.g. 80%), thefirst and second intake valve IV1, IV2 are set to Lo. V/T and inactiveV/T, respectively, and the EMA 29 is made active and controlled for theearly opening and late closing. This makes it possible to introduceinternal EGR in the medium-rotational speed/low-load region, to therebyreduce exhaust emissions.

Further, in an operating region I (medium-rotational speed/high-loadregion) in which the Ne value is equal to or higher than the fifthpredetermined value N5 and lower than the sixth predetermined value N6and the ACC value is equal to or higher than the fourth predeterminedvalue AC4, the first and second intake valves IV1, IV2 are set to Lo.VTand inactive V/T, respectively, and the EMA 29 is made active andcontrolled for the early opening. This makes it possible to increase thepower output in the medium-rotational speed/high-load region. Further,in an operating region J (high-rotational speed region) in which the Nevalue is equal to or higher than the sixth predetermined value N6, thefirst and second intake valves IV1 and IV2 are both set to Hi. V/T, andthe EMA 29 is made inactive. It should be noted that the aboveconfigurations are described only by way of example, and configurationsof operating regions, the valve timing of the first and second intakevalves IV1, IV2, and the active and inactive states of the EMA 29, aswell as a combination of these configurations can be changed asrequired.

It should be noted that the present invention is not limited to theembodiments described above, but can be embodied in various forms. Forexample, although in the embodiments, description is given of cases inwhich the invention is applied to the intake valves as the enginevalves, this is not limitative, but the invention may be applied toexhaust valves and the valve-closing timing thereof may be controlled.This enables the overlap amount to be variably controlled, therebyenhancing the power output and reducing exhaust emissions. Further,although in the present embodiment, as the actuator for holding theintake valve in the open state, the electromagnetic actuator isemployed, this is not limitative, but the invention can be applied toother types of actuators, such as a hydraulic type and an air-driventype.

Further, although in the embodiments, as one of the parameters fordefining an operating region of the engine 3 for determining theoperation mode of the EMA 29 etc., the accelerator opening ACC isemployed, this is not limitative, but in place of this, the intake pipeabsolute pressure, throttle valve opening, cylinder internal pressure,intake air amount, or other like parameters representative of load onthe engine 3, may be used. Further, although in the present embodiment,the switching mechanism for forcibly switching the EMA 29 to theinactive mode is formed by a hydraulic type, this is not limitative, butan electric or other type may be employed.

Moreover, although in the above embodiments, the cam-type valveactuating mechanism is employed in combination with the VTEC 13, this isnot limitative, but the present invention can be applied to a cam-typevalve actuating mechanism which is used in combination a cam phasevariable mechanism for continuously varying the cam phase, together withVTEC 13 or in place therewith.

INDUSTRIAL APPLICABILITY

As described heretofore, the valve control apparatus for an internalcombustion engine, according to the invention, actuates an engine valveby the cam-type actuating mechanism, and at the same time, depending onoperating conditions of the engine, the actuator is made active asrequired, whereby the closing timing of the engine valve can becontrolled as desired and optimally set. Further, when the actuator isinactive, the actuator is disconnected from the cam-type valve actuatingmechanism, whereby the engine valve can be opened and closed withoutincreasing the inertial mass of the engine valve. Therefore, the valvecontrol apparatus according to the invention can be suitably used in aninternal combustion engine which needs attaining the improvement of fueleconomy and realization of higher rotational speed and higher poweroutput in a compatible fashion, and reducing cost and weight thereof.

1. A valve control apparatus for an internal combustion engine forcontrolling opening and closing operations of an engine valve, the valvecontrol apparatus comprising: a cam-type valve actuating mechanism thatactuates said engine valve to open and close said engine valve, by a camwhich is driven in synchronism with rotation of said engine; an actuatorthat makes blocking engagement with said engine valve having beenopened, to thereby hold said engine valve in an open state; a rockershaft; an actuating rocker arm pivotally supported on said rocker shaft,for being brought into abutment with said engine valve and being drivenby said cam to actuate said engine valve to open and close said enginevalve; a holding rocker arm pivotally supported on said rocker shaft,for having said actuator brought into abutment therewith, to hold saidengine valve in the open state; operating condition-detecting means fordetecting operating conditions of said engine; a switching mechanism forswitching an operation mode of said actuator between an active mode inwhich said actuator makes the blocking engagement with said engine valveand an inactive mode in which said actuator does not make the blockingengagement with said engine valve, wherein said switching mechanismswitches the operation mode of said actuator between the active mode andthe inactive mode, by switching a state of said actuating rocker arm andsaid holding rocker arm between a connected state in which saidactuating rocker arm and said holding rocker arm are connected to eachother, and a disconnected state in which said actuating rocker arm andsaid holding rocker arm are disconnected from each other; operationmode-determining means for determining the operation mode of saidactuator according to the detected operating conditions of said engine;and control means for controlling operation of said actuator to therebycontrol closing timing of said engine valve; wherein said control meanscontrols operation of said actuator according to the detected operatingconditions of said engine and controls operation of said switchingmechanism according to the determined operation mode.
 2. A valve controlapparatus according to claim 1, wherein said actuating rocker armcomprises a plurality of actuating rocker arms, wherein the valvecontrol apparatus further comprises a first hydraulic switchingmechanism for hydraulically switching a state of said plurality ofactuating rocker arms between a connected state in which said pluralityof actuating rocker arms are connected to each other and a disconnectedstate in which said plurality of actuating rocker arms are disconnectedfrom each other, wherein said switching mechanism is formed by a secondhydraulic switching mechanism, wherein one of said plurality ofactuating rocker arms is formed with an oil chamber for said firsthydraulic switching mechanism, and wherein said holding rocker arm isarranged adjacent to said actuating rocker arm formed with said oilchamber.
 3. A valve control apparatus according to claim 1, wherein anabutment portion of said holding rocker arm with which said actuatorabuts is disposed at a location remoter from said rocker shaft than anabutment portion of said actuating rocker arm with which said enginevalve abuts is.
 4. A valve control apparatus according to claim 1,wherein an abutment portion of said holding rocker arm with which saidactuator abuts is disposed at a location closer to said rocker shaftthan an abutment portion of said actuating rocker arm with which saidengine valve abuts is.
 5. A valve control apparatus according to claim1, wherein said switching mechanism switches a state of said actuatingrocker arm and said holding rocker arm to a connected state when saidengine is in a low rotational speed condition, and to a disconnectedstate when said engine is in a high rotational speed condition.
 6. Avalve control apparatus for an internal combustions engine forcontrolling opening and closing operations of an engine valve, the valvecontrol apparatus comprising: a rocker shaft; an actuating rocker armpivotally supported on said rocker shaft, for being brought intoabutment with said engine valve and being driven by a cam which isdriven in synchronism with rotation of said engine, to thereby actuatesaid engine valve to open and close said engine valve; an actuator thatmakes blocking engagement with said engine valve having been opened, tothereby hold said engine valve in an open state; a holding rocker armpivotally supported on said rocker shaft, for having said actuatorbrought into abutment therewith, to hold said engine valve in the openstate; a switching mechanism for switching an operation mode of saidactuator between an active mode in which said actuator between an activemode in which said actuator makes the blocking engagement with saidengine valve and an inactive mode in which said valve actuator does notmake the blocking engagement with said engine valve, by switching astate of said actuating rocker arm and said holding rocker arm between aconnected state in which said actuating rocker arm and said holdingrocker arm are connected to each other, and a disconnected state inwhich said actuating rocker arm and said holding rocker arm aredisconnected from each and other; and control means for controllingoperation of said actuator to thereby control closing timing of saidengine valve.
 7. A valve control apparatus according to claim 6, furthercomprising operating condition-detecting means for detecting operatingconditions of said engine, and operation mode-determining means fordetermining the operation mode of said actuator according to thedetected operating conditions of said engine, and wherein said controlmeans controls operation of said switching mechanism according to thedetermined operation mode.
 8. A valve control apparatus according toclaim 6, wherein said switching mechanism is formed by a hydraulicswitching mechanism for hydraulically switching the operation mode ofsaid actuator, and wherein said control means causes said actuator to bemade inactive when said engine is started.
 9. A valve control apparatusaccording to claim 6, wherein said actuator is formed by anelectromagnetic actuator comprising; a single electromagnet that has acoil whose energization is controlled by said control means, an armaturethat is attracted to said electromagnet when said coil is energized, anda stopper provided integrally with said armature, for being brought intoblocking engagement with said engine vale having been opened, in a statein which said armature has been attracted to said electromagnet.
 10. Avalve control apparatus according to claim 6, further comprising ahydraulic impact-lessening mechanism that lessens an impact on saidengine valve caused by operation of said actuator.
 11. A valve controlapparatus according to claim 6, wherein said actuating rocker armcomprises a plurality of actuating rocker arms, wherein the valvecontrol apparatus further comprises a first hydraulic switchingmechanism for hydraulically switching a state of said plurality ofactuating rocker arms between a connected state in which said pluralityof actuating rocker arms are connected to each other and a disconnectedstate in which said plurality of actuating rocker arms are disconnectedfrom each other, wherein said switching mechanism is formed by a secondhydraulic switching mechanism, wherein one of said plurality ofactuating rocker arms is formed with an oil chamber for said firsthydraulic switching mechanism, and wherein said holding rocker arm isarranged adjacent to said actuating rocker arm formed with said oilchamber.
 12. A valve control apparatus according to claim 6, wherein anabutment portion of said holding rocker arm with which said actuatorabuts is disposed at a location remoter from said rocker shaft than anabutment portion of said actuating rocker arm with which said enginevalve abuts.
 13. A valve control apparatus according to claim 6, whereinan abutment portion of said holding rocker arm with which said actuatorabuts is disposed at a location closer to said rocker shaft than anabutment portion of said actuating rocker arm with which said enginevalve abuts.
 14. A valve control apparatus according to claim 6, whereinsaid switching mechanism switches a state of said actuating rocker armand said holding rocker arm to a connected state when said engine is ina low rotational speed condition, and to a disconnected state when saidengine is in a high rotational speed condition.